Generally, lock assemblies include a housing and a plug that form a lock cylinder and that define respective pin chambers to receive pin pairs. The pin pairs include outer pins substantially disposed within the housing, and inner pins disposed within the plug. Springs are often used to bias the pin pairs toward a key passageway defined in the plug. More specifically, the springs are engaged with the outer pins, which in turn engage the inner pins and force the inner pins into the key passageway. In the absence of a correct or proper key, the outer pins are partially disposed in the plug and block rotation of the plug within the housing.
The plug is rotatable relative to the housing in most conventional lock assemblies. A shear line is defined where the plug and the housing come together. When a proper or appropriate key is inserted into the key passageway, the inner pins are moved and, as a result, move the respective outer pins. The ends where the inner pins and the outer pins contact each other are aligned with the shear line upon insertion of the proper key, and allow the plug to be turned to a locked or unlocked position. In other words, the proper key will move the inner and outer pins such that the outer pins are disposed completely in the housing, and the inner pins are disposed completely in the plug.